The present invention relates to an arrangement in a pump block, the pump block including a plurality of pump valves, each connected to a piston in a piston pump, and an inlet pipe common to all of the pump valves, with one connection to each pump valve.
The type of pump block with which the arrangement according to the present invention may be employed exists in, for example, a high pressure pump or a homogenizer. A high pressure pump substantially consists of a powerful electric motor with transmission mechanism comprising belt rack, gearbox and crank mechanism housed in a crank housing. The high pressure pump also includes a pump section with the pump block, valves and pistons. The rotary motion from the electric motor is converted by means of the transmission mechanism into the reciprocating motion of the pistons.
A homogenizer is fundamentally a high pressure pump in which the pump block has been supplemented with one or more homogenizer devices or counterpressure devices in which the homogenization proper takes place. A high pressure pump or a homogenizer according to this principle is described in Swedish Patent Application SE 9800896-4.
Homogenization is an industrial process which has long been employed and whose purpose is to finely divide particles in different types of liquids, in order, for example, to stabilise emulsions, to promote flavour and aroma, to improve the colour saturation in paints, etc. A very common field of application is milk homogenization, whose purpose is to shear the largest fat globules occurring in the milk into smaller fat globules and by such means stabilise the fat emulsion, which prevents cream setting. The major proportion of all consumer milk today is homogenized.
Homogenization normally takes place in that, for example, a fat emulsion which may consist of milk is given a high input pressure which drives the emulsion at high speed through a very narrow gap where the fat globules of the fat emulsion are sheared, among other things as a result of the turbulence which occurs on a sudden pressure drop after the homogenization valve. The product which is to be homogenized is pressurized, often up to several hundred bar, by means of the high pressure pump and is forced to pass through a narrow gap in the counter pressure device.
When the product enters the homogenizer or high pressure pump, it passes in through an inlet pipe or duct and is distributed to the different valves in the pump block. In most homogenizers and high pressure pumps today, the inlet duct is drilled in the homogeneous pump block, which entails a high production cost. It also implies that it is not always possible to drill the inlet duct to such large diameters as is desirable. By selecting a large inlet diameter, the speed in the inlet pipe is reduced and thereby the risk of cavitation which may occur as a result of changes in speed arising out of the pulsation of the pump.
Attempts have been made to replace the inlet ducts drilled in the pump block by a separate inlet pipe. But since the product is often heated, very large thermal stresses may occur since the pipe is heated rapidly and the pump block, because of its large mass, is heated much more slowly. As regards homogenization, the product is often at a temperature of 75xc2x0 C. and the thermal stress which then may occur on start of the homogenizer exceeds the failure point level of the pipe material. High temperatures may also occur in the sterilization of the pipe or tube system before production begins. Naturally, the welds which must of necessity exist in the inlet pipe will crack at considerably lower thermal stress. The larger the homogenizer is, i.e. the greater the number of pump valves in the pump block, the larger will be the thermal stress which occurs between the pump block and the inlet pipe.
Solving this problem using expansion boxes or other expansive tube arrangements is unsuitable, since there is no room for these often bulky apparatuses and they are furthermore not suitable from the point of view of hygiene.
One object of the present invention is to realise an inlet pipe for a pump block which may be made as a separate part without the thermal stresses causing the pipe to crack.
A further object of the present invention is, by employing the arrangement according to the invention, to realise a considerably more economical inlet to the pump block which affords the possibility of freely selecting the diameter of the inlet.
These and other objects have been attained according to the present invention in that the arrangement of the type described by way of introduction has been given the characterizing feature that one of the connections between the pump block and the inlet pipe is fixed and that the other connections are movable in the longitudinal direction of the inlet pipe.
Preferred embodiments of the present invention have further been given the characterizing features as set forth in the appended subclaims